142 UNIVERSALITY OF DEGENERATIVE EVOLUTION 



Each phase in the evolution of this primitive 

 vertebra has been attended by degeneration. 



In man the vertebral column consists of : 

 (a) Seven cervical vertebrae. 

 (6) Three dorsal vertebrae, 

 (c) Five lumbar vertebrae. 

 (cT) Three sacral vertebrae. 

 (e) Six coccygeal vertebrae. 



Each one of these vertebrae exhibits important 

 modifications, and shows signs of degeneration. 

 The proatlas is represented by its intercentrum only. 

 The atlas consists of a centrum and neurapophyses, 

 but there is no zygapophyses ; it possesses one pair 

 of ribs and hsemapophyses in a reduced condition. 

 The axis consists of the same elements but carries 

 postzygapophyses. 



The four following cervical vertebrae consist of 

 the same elements, but carry both zygapophyses 

 and postzygapophyses. In man all the cervical 

 vertebrae, with the exception of the first (the 

 proatlas) have lost the intercentrum. The next 

 vertebrae which is generally regarded as the seventh 

 cervical vertebra, consists of the same elements, but 

 it ought to be regarded as the first dorsal vertebra. 

 The vertebral artery and the sympathetic nerve 

 trunks accompanying it, do not pass through the 

 vertebral canals ; in some cases these do not exist. 

 The so-called seventh cervical vertebra has occasion- 

 ally one fully developed rib which articulates with 

 the sternum like the ribs of true dorsal vertebrae. 



